feat: Complete Phase 4 error handling improvements for settings and onboarding

- Update settings page to use extractError() utility for consistent error messages
- Update onboarding page family creation/join with improved error handling
- Both pages now use centralized error extraction for user-friendly messages
- Preserves multilingual error messages from backend

Phase 4 Progress: 17/~20 forms completed (85%)
- ✅ Auth forms (login, register, forgot-password)
- ✅ Family & child management
- ✅ All 6 activity tracking forms
- ✅ Settings page (NEW)
- ✅ Onboarding flow (NEW)
- Note: Analytics/AI pages skipped - already have adequate error handling
- Note: PhotoUpload component skipped - already has proper error handling

Error improvement plan: ~85% complete (Phase 1-4 mostly done)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

maternal-web/app/(auth)/onboarding/page.tsx

@@ -40,6 +40,7 @@ import { useTheme } from '@mui/material/styles';
 import { StepIconProps } from '@mui/material/StepIcon';
 import { FamilySetupStep, ChildData } from '@/components/onboarding/FamilySetupStep';
 import { familiesApi } from '@/lib/api/families';
+import { extractError } from '@/lib/utils/errorHandler';
 
 const steps = ['Welcome', 'Preferences', 'Family Setup', 'Complete'];
 
@@ -230,7 +231,8 @@ export default function OnboardingPage() {
       setActiveStep((prev) => prev + 1);
     } catch (err: any) {
       console.error('Failed to create family:', err);
-      setError(err.response?.data?.message || 'Failed to create family. Please try again.');
+      const errorData = extractError(err);
+      setError(errorData.userMessage || errorData.message);
     } finally {
       setLoading(false);
     }
@@ -246,7 +248,8 @@ export default function OnboardingPage() {
       setActiveStep((prev) => prev + 1);
     } catch (err: any) {
       console.error('Failed to join family:', err);
-      setError(err.response?.data?.message || 'Failed to join family. Please check the code and try again.');
+      const errorData = extractError(err);
+      setError(errorData.userMessage || errorData.message);
     } finally {
       setLoading(false);
     }

maternal-web/app/settings/page.tsx

@@ -18,6 +18,7 @@ import { MeasurementUnitSelector } from '@/components/settings/MeasurementUnitSe
 import { TimeZoneSelector } from '@/components/settings/TimeZoneSelector';
 import { TimeFormatSelector } from '@/components/settings/TimeFormatSelector';
 import { PhotoUpload } from '@/components/common/PhotoUpload';
+import { extractError } from '@/lib/utils/errorHandler';
 import { motion } from 'framer-motion';
 import { useTranslation } from '@/hooks/useTranslation';
 import { useThemeContext } from '@/contexts/ThemeContext';
@@ -103,7 +104,8 @@ export default function SettingsPage() {
     } catch (err: any) {
       console.error('❌ Failed to save settings:', err);
       console.error('Error response:', err.response);
-      setError(err.response?.data?.message || err.message || 'Failed to save settings. Please try again.');
+      const errorData = extractError(err);
+      setError(errorData.userMessage || errorData.message);
     } finally {
       setIsLoading(false);
     }